Heavyweight champion Andy Ruiz Jr. was fighting kids nearly twice his age as a 7-year-old because nobody his age was big enough

Jimmy Kimmel Live! / YouTube

Heavyweight champion Andy Ruiz Jr. stunned the world on Saturday with his seventh-round TKO against Anthony Joshua.
Speaking with Jimmy Kimmel, Ruiz Jr. explained that he has been scoring surprising wins since his amateur days.
Due to his size as a child, Ruiz Jr. said he was fighting against 12- and 13-year-olds when he was just seven — and still beating opponents who were almost twice his age.
You can watch Ruiz Jr.’s entire appearance on the show below.
Visit Business Insider’s homepage for more stories.

Heavyweight champion Andy Ruiz Jr. stunned the world on Saturday with his seventh-round TKO against British bruiser Anthony Joshua.

Ruiz Jr.’s shot at the title came on short notice, stepping in just a few weeks before the fight to replace Jarrell Miller, Joshua’s scheduled opponent who failed three drug tests before the bout.

Looking at Ruiz Jr. and Joshua next to each other, it’s easy to see why Joshua was the heavy favorite, but Ruiz Jr.’s quick hands and beautiful combinations proved enough to take down the British superstar and become the first heavyweight champion of Mexican descent.

For Ruiz Jr., winning unlikely fights is nothing new. As he said on an appearance on "Jimmy Kimmel Live!" on Tuesday night, Ruiz Jr. has been fighting as an underdog since he started boxing as a child.

"I was six years old when I first went into a gym," Ruiz Jr. told Kimmel. "At my first amateur fight, I was seven years old. My dad took me to go fight San Diego. I was this big, heavy kid — nobody was at my weight at that age, so I had to fight 12-year-olds, 13-year-olds when I was seven years old. And what do you know, I was beating them."

"That had to make them think twice about a future in boxing, right?" Kimmel joked. "Getting beaten by a seven-year-old."

You can watch Ruiz Jr.’s entire appearance below.

Ruiz Jr. went on to explain that his win was a family affair, with his family members making nearly $10,000 after betting big on him to win as a heavy underdog.

As the heavyweight champion, Ruiz Jr. won’t be such a long shot next time he steps into the boxing ring, but whatever his odds are, the champ seems confident he can overcome them.

Read more from Tyler Lauletta:

Kawhi Leonard struggled to understand why his teammates weren’t as good as him in college

Khabib Nurmagomedov is officially set for his first fight since defeating Conor McGregor — and it comes against an opponent on a vicious 5-fight win streak

Obama took a small jab at Kobe Bryant while talking about Michael Jordan and the NBA Finals

Zlatan Ibrahimović scored a bicycle-kick goal so amazing he even impressed himself

NOW WATCH: Mount Everest is not the hardest mountain to climb — here’s what makes K2 so much worse